Portland cement manufacture
What is Portland cement? The Portland cement is the hydraulic cementing material that is grounded by the Portland cement clinker, 5%-20% mixed materials and certain content of gypsum. The Portland cement also called silicate cement, is a common cement used in civil engineering and construction.
As for the types of Portland cement, there is ordinary Portland cement, composite Portland cement, Portland slag cement, Portland fly-ash cement, etc. The ordinary Portland cement contains 5-20% active addition, other types of Portland cement generally contains more than 20% active addition.
How is Portland cement made?
STEP1: Crushing and pre-homogenization of Portland cement
In the portland cement production, most of raw materials should be crushed, such as limestone, clay, iron ore, coal and etc. The lime stone is the main raw material of Portland cement making, because its big size and high hardness, the lime stone crushing is more important in the cement crushing. The Portland cement pre-homogenization means that use stacker and recalimer to homogenize the raw material preliminary, the raw material yard plays double role in storage and homogenization.
STEP2: Portland cement raw materials
In general, at least three tons raw materials (including raw material, fuel, mixed materials, gypsum,etc.) is required for per ton of Portland cement manufacture. According to the statistic, the cement grinding plant consume more than 60% energy in the dry process cement production line, raw meal grinding takes 30% and above, so, to ensure cement quality and reduce energy, it is important to select cement grinding mill and cement grinding plant reasonably, optimize cement grinding process, control the operating system.
STEP3: Portland cement raw meal homogenization
The raw meal homogenizing is the last key to stabilize the raw meal of kiln feeding system, in the dry process cement production line, the stable raw meal of kiln feeding system is the premise of cement clinker plant thermal regulation.
STEP4: Preheating and precalcining of Portland cement
When the airflow carries the raw meal into the cyclone, it is forced to make a rotating flow in the annular space between the cyclone cylinder and the inner cylinder (exhaust pipe), and it moves downward while rotating, from the cylinder to the cone, and the movement can be extended to the end of the cone, and then turned upward to rotate upward, discharged by the exhaust pipe.
STEP5: Portland cement clinker production
After the preheating and precalcining, the qualified raw meal will be calcined and cement clinker is produced. We can generally divided the clinker production into six steps, including raw materials drying, raw materials dehydration, decarbonation, clinker cooling, sintering reaction and solid-phase reaction.
STEP6: Portland cement grinding
When the Portland cement clinker is ready, cement grinding plant process cement clinker into finished Portland cement. Then the finished cement can be stored in bulk or packed into bags.
Comparison of ordinary Portland cement and composite Portland cement?
The ordinary Portland cement and composite Portland cement has many differences in strength grade, mixing ratio of admixture, and etc.
Firstly, ordinary Portland cement has a minimum strength grade of 42.5, while composite Portland cement has a maximum strength grade of 32.5, which can be easily seen from the data.
Secondly, The admixture content of ordinary Portland cement is 5%-20%, while that of composite Portland cement include at least two types, with the content of 20%-50%.
ordinary Portland cement
High early strength, quick setting and hardening, good frost resistance, strong wear resistance, good construction performance; The heat of hydration is higher, poor heat resistance, poor chemical corrosion resistance of acid base and silicate.
Apply for overground projects, underground projects that are not subject to erosion, projects without water pressure, projects that are not subject to freezing in corrosion-free water, projects with good strength in the early stage, projects require a short time under low-temperature conditions.
composite Portland cement
Early strength and later strength is high, good workability, small bleeding, good water retention, low hydration heat, the concrete mixed by composite Portland cement is hard to crack, good construction performance, normal setting time, the strength and performance of composite Portland cement is basically consistent with that of ordinary Portland cement.
Widely apply for urban and rural construction, composite Portland cement can replace the use of ordinary Portland cement.